This invention relates to an eye refractive power measuring apparatus for measuring the eye refractive power of an eye under test by projecting a chart image for test use to the retina of the eye under test by using a visible light and judging the response of a patient.
Heretofore, there has been known the so-called subjective type in an eye refractive power measuring apparatus for measuring an eye under test, wherein a chart for test use is shown to a patient, a correction lens is moved to a position where the patient is supposed to see the chart correctly by judging the response of the patient, and the refractive power of the eye under test is measured from the refractive power of the correction lens. That is, a tester or oculist is required to effect the measurement based solely on the response of the patient and without his own recognition of the chart image on the retina of the eye.
By the way, in the eye refractive power measurement, it is not only required to measure refractive power but there is a case where it is required to measure how close to a near point position the eye under test can still enact its accommodation.
In such a case as mentioned above, according to the aforementioned conventional apparatus, the refractive power of the eye under test is corrected based on what is obtained by measurement, a chart for eyesight test use is moved to the near point position in the foregoing state, and amplitude of accommodation is measured by judging the response of a patient at that time.
There is also known another type of an eye refractive power measuring apparatus for both subjective and objective use, wherein the aforementioned subjective type refractive power measuring apparatus is incorporated in the so-called objective type refractive power measuring apparatus in which a measuring target image is projected to an eye under test by using invisible light and the refractive power of the eye under test is measured in an objective fashion by opto-electrically detecting the focusing state of the target image.
However, in any one of the above-mentioned conventional eye refractive power measuring apparatuses, the tester cannot observe the chart image for test use projected to the retina of an eye under test. Since the tester is required to carry out the test by guessing the patient's condition under which he gazes at the chart through question and answer exchanged between the tester and the patient, a long experience and a good perception are required in order to carry out an accurate measurement.
In the measurement for amplitude of accommodation, the amplitude of accommodation is measured based solely on the response of the patient, and the patient himself cannot know how far the accommodation is actually enacted, thus making it difficult to carry out an accurate measurement.